A stock banshee chassis is junk. You need a arms, shocks, stem and bars just for starters. That right there is about your budget. Then take those stock cylinders and let someone reputable to port them for you, buy some VF4 reeds, either mill the head or buy a head that allows dome changes. Find some decent carbs and for pipes that depends on porting. You won't need to go all out on the motor at first, but later on you will.
As stated, get the chassis "right" then worry about the motor.